At least nine people have died since Tropical Cyclone Kenneth, the strongest storm to hit the region since records began, made landfall in Mozambique on Thursday.
Five deaths were reported in Mozambique and another four in the island nation of Comoros, according to the United Nations Office for the Coordination of Humanitarian Affairs.
The cyclone is the second powerful tropical storm to hit southeast Africa in five weeks. Despite its power, Cyclone Kenneth is slow-moving, leading experts to fear it could continue to dump torrential rains on an area still reeling from the devastation wrought by Cyclone Idai.
That storm killed 750 people across southern Africa, forced thousands into camps in March and wreaked an estimated $1 billion worth of damage -- about 10% of Mozambique's GDP.
In the commercial hub and provincial capital of Pemba, residents Monday said they hoped the worst was over after a weekend of heavy rains and flooding since Cyclone Kenneth made landfall Thursday.
"The rain has stopped, at least for now. There is still water on the ground but the main roads in the city are now passable," said resident Innocent Mushunje.
Kevin Record, a hotel owner on the hard-hit island of Ibo, said the region was still without power and "waiting for the cavalry to arrive."
Forecasters said northern Mozambique could see up to 500 millimeters of rain (about 20 inches) over the next five days, which could exacerbate the flooding.
"The soil is saturated with rain and the rivers are already swollen, so the emergency is likely to get worse," said Michel Le Pechoux, UNICEF's deputy representative in Mozambique. "We're doing everything we can to get teams and supplies on the ground to keep people safe."
Save the Children said in a separate statement that the storm "has caused extensive damage, ripping homes apart and wiping out entire communities," and is warning that current conditions have made it extremely difficult to deliver aid to those in need.
"We have grave fears for the thousands of families currently taking shelter under the wreckage of their homes. They urgently need food, water and shelter to survive the coming days," said Nicholas Finney, Save the Children's response team leader in Mozambique.
Finney said that the NGO tried to reach some of the hard-hit areas Sunday but were forced to turn back "because rivers had burst their banks and the roads were under water."
"Flights and helicopters have also been grounded and this means humanitarian access is virtually impossible. We are desperately trying to look for ways to deliver emergency supplies," said Finney.
The United Nations' disaster response agency pledged to release $13 million to pay for food, shelter, health, water and sanitation assistance in both Comoros and Mozambique.
"The funds will help in reducing the suffering of the affected people including mitigating the impact on food security caused by the destruction and loss of farmland, livestock and fisheries, in addition to the damage and destruction of homes," said Mark Lowcock, the UN's emergency relief coordinator.
Mozambique's natural disaster management said last week that nearly 3,400 homes were destroyed and more than 18,000 were displaced by Kenneth.